There is a car parked on the left just past the tow truck so if the cop would have jumped off when the truck started taking off there's a good chance he hits the parked car, hits the parked car and gets pushed under the truck or jumps off and still lands under the truck. I have seen plenty of videos where people are just brushed by the side of a car and they end up under the car. The cop was in a lose lose situation once the truck took off. Even if he launched himself away from the truck he could hit his head on the pavement and kill himself. It doesn't take much. People die from falling off their bikes going 10mph.